The present invention relates to systems for detecting troubles in CMOS integrated circuits and, more particularly, to methods and systems for detecting troubles in CMOS integrated circuits on the basis of power supply current information.
Such CMOS integrated circuit trouble detection methods and systems have heretofore been used for quickly checking the normal operation of CMOS integrated circuits.
In a CMOS integrated circuit, only a very slight leak current flows as the supply current except for transient currents in transistor switching operations. This character of the CMOS integrated circuit can be utilized to detect troubles therein. A trouble is detected on the basis of a large current, which is not the transistor switching current or the leak current.
FIG. 11 shows a prior art example of the trouble detection system. In this case, a supply voltage is supplied from a power supply 5' to a CMOS integrated circuit 4' under test to check for a trouble in the circuit from the magnitude of the supply current, which is measured in an ammeter 6'.
FIG. 12 shows another prior art example of the trouble detection system. In this case, a tester 1 applies a test pattern from a test pattern storage unit 3 to a CMOS integrated circuit 4 under test, and the supply current at this time is detected in a current detection unit 6. A checking unit 7 checks for a trouble in the circuit 4 from the result of the detection or observation.
FIG. 13 shows a method of current measurement carried out in an IC checking system for checking electric characteristics of ICs (integrated circuits) proposed in Japanese Laid-Open Patent Publication No. 2-302677. In this method, current is measured in a timed relation to a generated test pattern. Specifically, for accurate current measurement a test pattern 102 which is outputted from a test pattern generator, is utilized to generate a gate signal for controlling the measurement of the supply current 101 in synchronism to the test pattern.
In the CMOS integrated circuit trouble detection system as shown in FIG. 11, which is based on the current measurement, the supply current in the CMOS integrated circuit is measured in the inoperative state thereof. Therefore, it is not always possible to measure a supply current in the case of a trouble.
The case of FIG. 12 is the real-time measurement of the supply current by operating the CMOS integrated circuit using the tester. However, it takes a time to detect current. That is, the real-time supply current measurement substantially cannot be made depending on the CMOS integrated circuit under test; it cannot be made with, for instance, high frequency operation devices or the like.
The prior art method of current measurement is applied to a system of determining AC characteristics of the supply current in a CMOS integrated circuit in the operative state thereof. In the system, the CMOS integrated circuit is tested by applying test patterns thereto and measuring the supply current therein for each applied test pattern. The accurate measurement of the supply current, however, requires a high speed current measuring system, and it is difficult in a short period of time.
FIG. 14 illustrates conceivable measurement of a quiescent current 105 caused as the supply current which is not a transistor switching current in a CMOS integrated circuit. In this case, however, it is necessary to separate the quiescent current from the supply current 106 as the transistor switching current, but it is difficult to do so.